How to recognize mouse location on map in the picture box? - vb.net

Question

I have a country map in a picture box with provincial divisions. I can fill each province on mouse over by calling following floodfill function on my pictureBox MouseMove event:
Private Structure BITMAPINFOHEADER
Dim biSize As Integer
Dim biWidth As Integer
Dim biHeight As Integer
Dim biPlanes As Short
Dim biBitCount As Short
Dim biCompression As Integer
Dim biSizeImage As Integer
Dim biXPelsPerMeter As Integer
Dim biYPelsPerMeter As Integer
Dim biClrUsed As Integer
Dim biClrImportant As Integer
End Structure
''' <summary>
''' API declarations
''' </summary>
''' <param name="hdc"></param>
''' <returns></returns>
''' <remarks></remarks>
Private Declare Function CreateCompatibleDC Lib "gdi32" (ByVal hdc As IntPtr) As IntPtr
Private Declare Function CreateDIBSection Lib "gdi32" (ByVal hdc As IntPtr, ByRef pBitmapInfo As BITMAPINFOHEADER, ByVal un As Integer, ByRef lplpVoid As IntPtr, ByVal handle As Integer, ByVal dw As Integer) As IntPtr
Private Declare Function BitBlt Lib "gdi32" (ByVal hDestDC As IntPtr, ByVal x As Integer, ByVal y As Integer, ByVal nWidth As Integer, ByVal nHeight As Integer, ByVal hSrcDC As IntPtr, ByVal xSrc As Integer, ByVal ySrc As Integer, ByVal dwRop As Integer) As Integer
Private Declare Function ExtFloodFill Lib "gdi32" (ByVal hdc As IntPtr, ByVal X As Integer, ByVal Y As Integer, ByVal crColor As Integer, ByVal wFillType As Integer) As Integer
Private Declare Function CreateSolidBrush Lib "gdi32" (ByVal crColor As Integer) As IntPtr
Private Declare Function GetPixel Lib "gdi32" (ByVal hdc As IntPtr, ByVal X As Integer, ByVal Y As Integer) As Integer
Private Declare Function SelectObject Lib "gdi32" (ByVal hdc As IntPtr, ByVal hObject As IntPtr) As IntPtr
Private Declare Function DeleteObject Lib "gdi32" (ByVal hObject As IntPtr) As Integer
Private Declare Function DeleteDC Lib "gdi32" (ByVal hdc As IntPtr) As Integer
Private Declare Function GdiFlush Lib "gdi32" Alias "GdiFlush" () As Integer
Private Const SRCCOPY = &HCC0020
Public Sub FloodFill(ByRef mbmp As Bitmap, ByVal col As Color, ByVal Pt As Point)
If mbmp Is Nothing Then Exit Sub
Dim srcDC As IntPtr = CreateCompatibleDC(IntPtr.Zero)
Dim dstDC As IntPtr = CreateCompatibleDC(IntPtr.Zero)
Dim dstBMI As BITMAPINFOHEADER
With dstBMI
.biBitCount = 24
.biHeight = mbmp.Height
.biSize = System.Runtime.InteropServices.Marshal.SizeOf(dstBMI)
.biWidth = mbmp.Width
.biPlanes = 1
End With
Dim dstBits As IntPtr
Dim mbmpGetHbitmap As IntPtr = mbmp.GetHbitmap
'Select the bitmap into an HDC
Dim Obmp As IntPtr = SelectObject(srcDC, mbmpGetHbitmap)
'Create a DIB
Dim dstBMP As IntPtr = CreateDIBSection(dstDC, dstBMI, 0, dstBits, 0, 0)
Dim Obmp2 As IntPtr = SelectObject(dstDC, dstBMP)
'Place our bitmap in the DIB
BitBlt(dstDC, 0, 0, mbmp.Width, mbmp.Height, srcDC, 0, 0, SRCCOPY)
GdiFlush()
'Create a brush to use to FloodFill
Dim mBrush As IntPtr = CreateSolidBrush(System.Drawing.ColorTranslator.ToOle(col))
Dim hmm As IntPtr = SelectObject(dstDC, mBrush)
'Label5.Text = mBrush
'Fill with color
ExtFloodFill(dstDC, Pt.X, Pt.Y, GetPixel(dstDC, Pt.X, Pt.Y), 1)
'Get the bitmap back with the Filled Color
mbmp = Bitmap.FromHbitmap(dstBMP)
'Go berserk clearing memory
'ExtFloodFill has a bad reputation for gobbling up memory
'if you dont clean up properly
DeleteObject(mBrush)
DeleteObject(SelectObject(dstDC, mBrush))
DeleteObject(SelectObject(dstDC, dstBMP))
DeleteObject(SelectObject(srcDC, mbmpGetHbitmap))
DeleteObject(hmm)
DeleteObject(dstBits)
DeleteObject(Obmp2)
DeleteObject(Obmp)
DeleteObject(dstBMP)
DeleteDC(dstDC)
DeleteDC(srcDC)
mbmpGetHbitmap = Nothing
hmm = Nothing
dstBits = Nothing
Obmp2 = Nothing
Obmp = Nothing
dstBMP = Nothing
dstDC = Nothing
srcDC = Nothing
dstBMI = Nothing
End Sub
the only thing I need is to recognize floodfilled province on mouse over. any suggestion?

Answer 1

If you know the map coordinates you could do bounds checking on a defined list of rectangles.
i.e. a class which has a name as string and a rectangle
so washington might be (0,0,100,100)
and new york might be (100,40,100,100)
then just look through your list of objects and bounds check them
return the "name" of the area to the user
if that is what you were trying to achieve.
p.s. i'm not sure why you're using alot of "classic" blitting / GDI code where the .NET framework system.drawing namespace could be much nicer for you....
dim b as New Bitmap(Width, Height, Imaging.PixelFormat.Format32bppPArgb)
dim g as graphics = graphics.fromimage(b)
g.Clear(Color.White)
g.DrawImage(Bitmap.FromFile("test.jpg"), New Rectangle(0, 0, 100, 100))
PictureBox1.image = b